U.S. patent number 9,279,411 [Application Number 13/243,277] was granted by the patent office on 2016-03-08 for method for operating a wind turbine.
This patent grant is currently assigned to ALOYS WOBBEN. The grantee listed for this patent is Alfred Beekmann, Wolfgang De Boer. Invention is credited to Alfred Beekmann, Wolfgang De Boer.
United States Patent |
9,279,411 |
Beekmann , et al. |
March 8, 2016 |
Method for operating a wind turbine
Abstract
The invention concerns a method of operating a wind power
installation. The wind power installation has a circuit for
measuring the frequency prevailing in the electrical supply network
connected to a control device for controlling operation of the wind
power installation. It is proposed that the power delivered by the
generator of the wind power installation to the network is
increased quickly and for a short period above the currently
prevailing power of the wind power installation if the network
frequency of the electrical network is below the desired target
frequency of the network by a predetermined frequency value.
Inventors: |
Beekmann; Alfred (Wiesmoor,
DE), De Boer; Wolfgang (Moormerland, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Beekmann; Alfred
De Boer; Wolfgang |
Wiesmoor
Moormerland |
N/A
N/A |
DE
DE |
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Assignee: |
ALOYS WOBBEN (Aurich,
DE)
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Family
ID: |
42663923 |
Appl.
No.: |
13/243,277 |
Filed: |
September 23, 2011 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20120104756 A1 |
May 3, 2012 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/EP2010/053760 |
Mar 23, 2010 |
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Foreign Application Priority Data
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Mar 23, 2009 [DE] |
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10 2009 014 012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J
3/241 (20200101); F03D 7/0284 (20130101); F03D
7/0224 (20130101); F03D 9/255 (20170201); H02P
9/00 (20130101); F03D 7/048 (20130101); H02J
3/381 (20130101); F03D 9/257 (20170201); H02P
9/105 (20130101); F03D 7/0272 (20130101); F03D
1/06 (20130101); H02P 2101/15 (20150115); F05B
2240/96 (20130101); F05B 2270/337 (20130101); H02J
2300/28 (20200101); F05B 2270/1033 (20130101); Y02E
10/76 (20130101); Y02E 10/72 (20130101); F05B
2270/1041 (20130101); F05B 2270/309 (20130101) |
Current International
Class: |
H02P
9/00 (20060101); H02J 3/38 (20060101); F03D
7/04 (20060101); H02P 9/10 (20060101); H02J
3/24 (20060101); F03D 7/02 (20060101) |
Field of
Search: |
;307/153 ;290/44,55 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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469-1987 |
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CL |
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1410669 |
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Apr 2003 |
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CN |
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101054951 |
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Oct 2007 |
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CN |
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10341504 |
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Jun 2005 |
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DE |
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102005052011 |
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May 2007 |
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DE |
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1 467 463 |
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Oct 2004 |
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EP |
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1 790 850 |
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May 2007 |
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EP |
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1 914 419 |
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Apr 2008 |
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EP |
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1914419 |
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JP |
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JP |
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Nov 2008 |
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JP |
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2 073 310 |
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Feb 1997 |
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RU |
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1163457 |
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Jun 1985 |
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SU |
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94/27361 |
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Nov 1994 |
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WO |
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00/73652 |
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Dec 2000 |
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WO |
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01/86143 |
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Nov 2001 |
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WO |
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0186143 |
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Nov 2001 |
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WO |
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03/023224 |
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Mar 2003 |
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WO |
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2008/040350 |
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Apr 2008 |
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WO |
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Primary Examiner: Fureman; Jared
Assistant Examiner: Perez Borroto; Alfonso
Attorney, Agent or Firm: Seed IP Law Group PLLC
Claims
The invention claimed is:
1. A method of operating a wind power installation, wherein the
wind power installation is connected to an electrical supply
network and in operation or when wind prevails above an initial
speed and below a switch-off speed, the wind power installation
feeds electrical energy into the supply network, and the electrical
energy has a frequency and voltage desired or required by the
supply network, wherein in operation of the wind power installation
above its rated value or below a switch-off speed a rotor of the
wind power installation that has at least one rotor blade that
rotates, and connected to the rotor of the wind power installation
is a generator driven by the rotor thereby to generate electrical
energy, the method comprising: measuring the frequency prevailing
in the electrical supply network; transmitting the measured network
frequency to a control device for controlling operation of the wind
power installation; and controlling for a limited period, the power
delivered by the generator of the wind power installation above the
currently prevailing power of the wind power installation when the
network frequency of the supply network is below a target frequency
of the supply network by a predetermined frequency value or when
the network frequency falls with a frequency gradient greater than
a threshold value, wherein the frequency gradient is a change in
relation to time that exceeds a predetermined amount of change,
wherein controlling comprises: in a deadband range, wherein the
network frequency is in a frequency range between a rated frequency
for the supply network and a deadband frequency, the power is not
increased, in a control-band range, wherein the network frequency
is in a frequency range between the deadband frequency and a
control-band frequency, the power is increased based on a frequency
deviation of the network frequency from the deadband frequency, and
in an under-frequency range, wherein the network frequency is less
than the control-band frequency, the power is increased by a preset
power that is a maximum power increase supplied in the control-band
range and determined based on a maximum frequency deviation in the
control-band range.
2. The method according to claim 1 wherein the predetermined
frequency value is within the range of greater than 0.1% and less
than 2% of the network target frequency.
3. The method according to claim 1 wherein the power increase is
effected utilizing rotational energy stored in the moment of
inertia of the rotor of the wind power installation.
4. The method according to claim 1 wherein the frequency of the
power fed into the network always corresponds to the currently
prevailing network frequency, that is to say the power which is fed
in set to a frequency below the network frequency if the network
frequency is less than the target value of the network
frequency.
5. The method according to claim 1 wherein the increase in power is
effected above the rated power, when the feed was previously
effected with a rated power.
6. The method according to claim 1 wherein within a threshold
period of time after the frequency value falls below the
predetermined frequency value of the network frequency or after the
predetermined amount of change is exceeded, the power increase is
effected.
7. The method of controlling a wind park comprising at least two
wind power installations, in which each wind power installation is
controlled in accordance with a method according to claim 1,
wherein the increase in the power to be delivered to the network
from all wind power installations is unitarily and/or centrally
controlled.
8. A wind power installation adapted to carry out the method
according to claim 1.
9. A wind park wherein the wind park includes a plurality of wind
power installations adapted to carry out a method according to
claim 7.
10. The method according to claim 1 wherein the predetermined
frequency value is within the range of 0.1 Hz and 1.0 Hz.
11. The method according to claim 1 wherein the predetermined
amount of change is in the range of 0.5 Hz/second to 2
Hz/second.
12. The method according to claim 6 wherein the threshold period of
time is 10 to 1000 ms after the frequency value falls below the
predetermined frequency value of the network frequency.
13. The method according to claim 6 wherein the threshold period of
time is within the range of 50 to 100 ms, after the frequency value
falls below the predetermined frequency value of the network
frequency.
14. The method according to claim 6 wherein the increased power is
provided for a threshold amount of time.
15. The method according to claim 14 wherein the threshold amount
of time is in the range of 0.5 seconds to 30 seconds.
16. The method according to claim 14 wherein the threshold amount
of time is in the range of 1 second to 10 seconds.
17. A method of providing increased power to an electrical network
from a wind power installation comprising: sensing a network
frequency of the electrical network; determining whether the
network frequency falls within a deadband range in which the
network frequency is in a frequency range between a rated frequency
for the network and a deadband frequency, in a control-band range,
wherein the network frequency is in a frequency range between the
deadband frequency and a control-band frequency, or in an
under-frequency range, wherein the network frequency is less than
the control-band frequency, an exciter current is increased by a
preset power; increasing the exciter current of a generator of the
wind power installation within a selected time period when the
network frequency falls greater than a threshold value; and
extracting for a period of time more power from wind power
installation than the current power being produced without a
corresponding increase in the wind speed, wherein when the network
frequency is in the deadband range, the more power is not
extracted, wherein when the network frequency is in the
control-band range, the more power is extracted based on a
frequency deviation of the network frequency from the deadband
frequency, and wherein when the network frequency is in the
under-frequency range, the more power is extracted by the preset
power that is a maximum extracted power in the control-band range
and determined based on a maximum frequency deviation in the
control-band range.
18. The method according to claim 17 wherein the threshold value is
a percentage of the normal network frequency.
19. The method according to claim 18 wherein the threshold value is
in the range of 0.2% and 3.0% of the normal network frequency.
20. The method according to claim 17 wherein the threshold value is
a rate of decline over time from the normal network frequency.
21. The method according to claim 17 wherein the selected time
period is within the range of 0.02 seconds and 1 second.
22. The method of according to claim 17 wherein the selected time
period is within the range of 2 seconds to 12 seconds.
23. The method according to claim 22 wherein the selected time
period is less than 8 seconds.
24. A method of controlling a single wind turbine comprising:
producing a selected amount of power from the wind turbine based at
least in part on the rotation speed of a rotor mechanism as driven
by the wind; outputting the selected amount of power from the wind
turbine onto an electrical network; sensing the frequency of the
electrical network onto which the selected amount of power is being
output; and controlling an amount of electrical power output from
the wind turbine to the electrical network when the frequency of
the network falls below a selected value by converting some of the
inertia in the rotor mechanism to electrical power, thus briefly
reducing its rotation speed, wherein: in a deadband range, wherein
the network frequency is in a frequency range between a rated
frequency for the network and a deadband frequency, the electrical
power output from the wind turbine to the electrical network is not
increased, in a control-band range, wherein the network frequency
is in a frequency range between the deadband frequency and a
control-band frequency, the electrical power output from the wind
turbine to the electrical network is increased based on a frequency
deviation of the network frequency from the deadband frequency, and
in an under-frequency range, wherein the network frequency is less
than the control-band frequency, the electrical power output from
the wind turbine to the electrical network is increased by a preset
power that is a maximum power increase supplied in the control-band
range and determined based on a maximum frequency deviation in the
control-band range.
Description
BACKGROUND
1. Technical Field
The invention concerns a method of operating a wind power
installation and a wind power installation for carrying out the
method.
2. Description of the Related Art
As state of the art attention is directed in particular to `Grid
Integration of Wind Energy Conversion Systems`, Siegfried Heier,
1998, therein in particular pages 263 and so forth as well as U.S.
Pat. No. 7,345,373 and WO 01/86143.
The most relevant state of the art is document WO 01/86143.
That document discloses the teaching of reducing the power of a
wind power installation when the network frequency, that is to say
the frequency of the network into which the wind power installation
feeds its electrical power, exceeds a given value above the target
frequency.
In the case of Central European networks the target frequency is
usually at 50 Hz whereas in the case of US networks it is at 60 Hz.
The network is also referred to as the grid or power grid.
At the same time however there are also sometimes slight network
frequency fluctuations which are dependent on how greatly the ratio
of the power produced by the energy producers connected to the
electrical network is balanced out in relation to the power taken
by the consumers, that is to say those who are connected to the
electrical network and take electrical energy in order therewith to
operate any electrical equipment.
If, for example, the power supply from the generators is above that
which the consumers connected to the network are taking in terms of
power, the network frequency rises. Conversely the frequency can
also fall below the target frequency, for example below 50 Hz, if
the power supply offered is less than that which is being taken by
the electrical consumers connected to the network.
Network management, that is to say the management of producers and
also large consumers, is usually implemented by the network
operators. In that case network management can provide quite
different regulating mechanisms, for example for automatically
switching on certain generators (for example gas fired power
stations), automatic switch-off of given large consumers or also
the use of pumped storage plants and the like. In normal operation
even the network management of large supply networks constantly
succeeds in keeping the network frequency in the region of the
target frequency, in which respect minor deviations are certainly
allowed. Those minor deviations however should generally not exceed
the region of +0.1%. It will be appreciated that the network
management can also involve switching on further networks which are
connected to the network in order thereby to feed additional power
into the network or to take it from the network and feed it into
other networks.
For wind power installations, document WO 01/086143--as already
stated above--already teaches reducing the power below the
currently available power if a given network frequency value is
exceeded, for example a value which is 3.Salinity. above the target
value of the network frequency (for example over 50 Hz).
The document, WO01/086143, further teaches that, if the frequency
continues to rise, the power is linearly further reduced, in
dependence on the further rise in the network frequency.
BRIEF SUMMARY
One object of the present invention is to improve the operation of
a wind power installation in comparison with the state of the art
and overall to improve the network support of the wind power
installation with respect to the network.
One way to achieve that object is attained by a method having the
features of claim 1. Advantageous developments and further
embodiments are described by the appended claims.
According to the invention the wind power installation is not
switched off on the initial fall of a given frequency value below
the target value of the network frequency, but the wind power
installation continues to be operated, with an increased power.
Quickly, and for a short period, the power is higher than the power
which was previously fed into the network. For that purpose for
example the rotational energy stored in the moment of inertia of
the rotor and generator system is used, that is to say more power
is taken briefly from the entire rotor and generator system so that
an increased level of power is quickly available immediately upon
the network frequency falling below the predetermined target value.
This delivery of increased power can also occur when the wind power
installation had previously fed in at rated power, that is to say
it had delivered its normal maximum amount, namely all the power
that it can take from the wind under normal operating
conditions.
The amount by which the power is quickly increased is in a range of
up to 10 to 30% of the rated power, preferably about 20% of the
rated power.
The predetermined frequency value can be established in one example
by presetting a deadband frequency. As soon as the network
frequency is below that deadband frequency, the currently
prevailing output power of the wind power installation is raised
and the power delivered by the wind power installation, and fed
into the network, is also raised. The deadband frequency is
selected to be below the desired target frequency of a network by
the predetermined frequency value.
The predetermined frequency value is preferably greater than 0.1%,
0.2% or 0.3% of the network target frequency, according to
respective alternative embodiments. In the case of a 50 Hz network
target frequency therefore the system detects when the value falls
below the frequency of 49.95 Hz, 49.90 Hz and 49.85 Hz
respectively.
Alternatively, or in addition, a relative frequency change can also
be considered, that is to say a relative frequency drop also
denoted by df/dt or a frequency gradient. If the magnitude of such
a network frequency change in relation to time is excessively great
and therefore the frequency falls excessively quickly the power
which is currently to be fed into the network can be briefly
increased to support the network. Detecting such a frequency change
in relation to time, that is to say df/dt, may make it possible to
more rapidly detect a network frequency drop and thus possibly
permits faster recognition of the need for network support.
Detection of an absolute frequency value, that is to say when the
value falls below an absolute predetermined frequency value, and
also the change in relation to time, can also be combined. Thus for
example it is possible for a fast network frequency drop to be
assessed as less critical if the absolute value of the network
frequency is above the rated frequency.
If in addition or also as an alternative a frequency gradient is
detected, it has proven to be desirable to provide for a power
increase as from a gradient of 0.1 Hz/s. An amount of change, that
is to say a gradient of 0.2-7 Hz/s, in particular 0.5-2 Hz/s, has
proven to be an advantageous range for initiating a power increase.
Thus for example 0.2 Hz/s, 0.5 Hz/s, 1 Hz/s, 2 Hz/s and 5 Hz/s are
advantageous values. It is to be noted that the detection of a
frequency gradient of for example 1 Hz/s usually does not
presuppose any measurement over the period of an entire second.
Rather, measurement times of 20 ms and less, in particular 10 ms,
are suitable measurement times. Shorter measurement times of for
example 5 ms or even shorter are also preferred values. In addition
both the measurement time and also the underlying amount of change
or the underlying frequency gradient can depend on the network
target frequency. The above-mentioned values for the frequency
gradient and the measurement times provided for same relate to a 50
Hz target frequency. In the case of a 60 Hz target frequency a
somewhat greater gradient and/or a somewhat shorter measurement
time can possibly be provided.
It is also to be mentioned that the short-term power increase can
also be used to stabilize or smooth the network frequency or to
damp frequency fluctuations. In particular damping of frequency
fluctuations can advantageously take account of the frequency
gradient.
Preferably the short-term power increase is effected, utilizing the
rotational energy stored in the moment of inertia of the
rotor/generator system. That therefore concerns taking kinetic
energy which is stored both in the rotating rotor which has one or
more rotor blades, and also in the rotating rotor member of the
generator. Taking a higher amount of power can be implemented in
particular by increasing the exciter current and thus by increasing
the generator counter-moment of the generator rotor member. In
particular gearless generators with rotor members of large diameter
and thus large masses and correspondingly large moments of inertia
can store a considerable amount of kinetic energy.
Preferably the frequency of the power fed into the network always
corresponds to the currently prevailing network frequency. If
therefore the network frequency drops, a power increase can be
effected, in which case however the frequency of the feed into the
network is reduced, adapted to the currently prevailing
frequency.
Preferably there is proposed a method characterized in that the
increase in the power is effected above the currently prevailing
power, that is to say also above the rated power, when previously
the feed into the network was with rated power. Therefore, even
when the wind power installation is operated in the rated mode, a
power increase is effected upon a critical drop in frequency. In
that respect, it was realized that a rated power which can usually
also represent a maximum power at any event for ongoing operation
can be exceeded for short-term network support without damage to
the wind power installation.
In an embodiment it is proposed that the method is characterized in
that within a period of 10 to 1000 ms, in particular 20 to 500 ms,
preferably 50 to 100 ms, after the frequency value falls below the
predetermined frequency value of the network frequency or after the
predetermined amount of change is exceeded the power increase to
the network is effected. The feed to the network from the wind
turbine is effected with an increased power, that is to say a power
which is above the previously supplied power, for a period of time
of at least 0.5 sec, preferably at least 1 sec to a maximum of 30
sec. Preferably the power is increased for a set amount of time,
such as at about 3 to 6 seconds or, 8, 10, 12 or 15 seconds. In
principle a reaction time which is as short as possible, of for
example 10 ms, is to be viewed as an preferred value for
implementing an increase in power. In particular the time of 10 ms
corresponds to a half-wave at a network frequency of 50 Hz. A
longer response time of up to 1 sec is desirable to prevent an
over-reacting or indeed unstable system. In particular, reaction
time values of 50 to 100 ms have proven to be an advantageous
compromise.
The power increase is required in principle for a short period of
time. That period of time usually lasts for at least 0.5 sec but
preferably 1 sec and goes up to 3, 6, 8, 10, 12, 15 and a maximum
of 30 sec. If an increased power feed of more or markedly more than
10 sec is required, that is no longer generally to be viewed as an
instantaneous support measure, but rather an increased power
requirement. An effective range for the power increase has proven
to be at 3 to 6, 8, 10, 12 or 15 sec.
Preferably there is provided a method of controlling a wind park in
which each wind power installation is controlled in accordance with
a method according to the invention. In particular each wind power
installation is adapted to deliver an increased level of power to
the network in the case of a frequency dip. In that respect a wind
park includes at least two wind power installations but usually
markedly more installations like 10 wind power installations, 50
wind power installations or even more. Among all wind power
installations in the wind park however only those which are also
involved in the described method are to be considered.
Preferably in this case too the increase in the power delivered to
the network from all wind power installations is effected in
unitary and/or central relationship. On the one hand that prevents
different installations of a wind park responding at different
times and possibly impeding each other. In addition wind parks can
be subject to certain conditions such as limit values for coupling
to the network if the wind park feeds the power of all wind power
installations into the network at a network connection location.
Thus for example upper limits for the power fed into the network on
the part of the connection line can however possibly also be preset
when using a central transformer for same. A central control can
take account of such boundary conditions. Sometimes a unitary
control of the wind power installations can be helpful, if that is
possible with different wind power installations in a wind park.
Thus it is possible to implement at least partially unitary control
for example in regard to the response times and/or periods of the
power increase. If for example in a situation where all or most
wind power installations of a wind park are in the rated mode of
operation a power increase of all wind power installations should
be limited because of a power feed upper limit for the wind park,
the control can be effected in such a way that firstly a group of
the wind power installations contribute to a power increase and
thereafter another group of the wind power installations do so. In
addition the level of control and regulating complication and
expenditure can be reduced by a central control unit which only
delivers the corresponding power target values to each wind power
installation in the wind park for example for a power increase. For
example, in a case where a wind park includes 50 wind turbines, if
the frequency dips then 10 of the wind turbines can provide
increased power. Then, if 3 to 6 seconds have passed and the
frequency has returned to normal, no further action need be taken.
But, if 3 to 6 seconds pass and the frequency is still below the
threshold value, then another set of 10 wind turbines of the 50 can
provide increased power. Then, if another 3 to 6 seconds pass and
the frequency is not restored to the proper value, another 10 wind
turbines can provide increased power, and so on.
In addition there is proposed a wind power installation adapted to
use a method according to the invention. Furthermore there is
proposed a wind park which includes a plurality of wind power
installations according to the invention and preferably uses a
central control method and/or in which the increase in the power of
the wind power installations, that is to be delivered to the
network, is at least partially unitarily controlled. Central
control for the increase in the power to be delivered to the
network from all wind power installations can be implemented by a
separate central control unit and/or a wind power installation can
function as a master so that the other wind power installations
depend on that installation. In principle it is also possible for a
wind park to be divided into a plurality of park portions, in
regard to control procedures, in order for example to bundle
together installations of the same or a similar type in each case,
in terms of control procedures.
To increase the power delivery, not only is utilization of the
rotational energy of the moment of inertia considered, but also as
a support or possibly exclusively, it is possible to effect a
change in the setting angle of the rotor blades--a change in the
pitch angle, referred to as pitching--to increase the wind yield.
That is effected in particular when the wind power installation is
running under rated load, that is to say is already delivering
rated power, and in particular the rotor blades have already been
partially pitched to regulate the rated rotary speed.
After a power increase the speed of rotation of the rotor can have
reduced because kinetic energy has been taken. Particularly in the
event of a power increase in the case of a rated load mode of
operation, such a reduction can however be less or may not occur at
all. A reduction in rotary speed is to be expected in particular in
the part-load range and then depends on the level and duration of
the power increase, that is to say the power which is additionally
delivered.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The invention is described in greater detail hereinafter by means
of embodiments by way of example with reference to the accompanying
Figures.
FIG. 1 diagrammatically shows a partly opened pod of a wind power
installation with a diagrammatic view of the hub and parts of the
generator,
FIG. 2 diagrammatically shows an overview with a gearless
rotor/generator coupling arrangement with frequency
measurement,
FIG. 3 shows an embodiment by way of example of a power/frequency
characteristic of a wind power installation,
FIG. 4 shows an alternative embodiment to FIG. 3,
FIG. 5 shows an example illustrating power configurations for a
constant power increase,
FIG. 6 shows an example illustrating power configurations in the
event of a power increase which is effected in dependence on the
rotary speed of the rotor,
FIG. 7 shows an example illustrating measurement of a power in the
case of a power increase dependent on the rotary speed of the
rotor,
FIG. 8 shows measurement of a power with a constant power increase,
and
FIG. 9 shows possible variations in the power values by which a
power increase is to be implemented in dependence on the frequency
and for different adjustable maximum values in respect of the power
increase.
DETAILED DESCRIPTION
Hereinafter identical references can denote identical components
but also components which are similar and not identical.
Hereinafter, for the sake of completeness, a wind power
installation having a synchronous generator and a gearless design
with a full-wave converter is described.
FIG. 1 diagrammatically shows a pod 1 of a gearless wind power
installation. The hub 2 can be seen by virtue of the housing, also
called the spinner, pod or nacelle, being shown partly open. Three
rotor blades 4 are fixed to the hub, the rotor blades 4 being shown
only in their region near the hub. The hub 2 with the rotor blades
4 forms an aerodynamic rotor 7. The hub 2 is mechanically fixedly
connected to the generator rotor 6, which can also be referred to
as the rotor member 6 and is referred to hereinafter as the rotor
member 6. All parts that rotate are referred to herein jointly as
the rotor assembly. The rotor member 6 is mounted rotatably with
respect to the stator 8.
During its rotation relative to the stator 8 the rotor member 6 is
supplied with current, usually a direct current, in order thereby
to generate a magnetic field and build up a generator moment or
generator counter-moment which can also be suitably set by that
exciter current and can be altered. When the rotor member 6 is thus
electrically excited its rotation relative to the stator 8 produces
an electrical field in the stator 8 and thus an electrical
alternating current.
In the example just described, the exciter current is in the rotor.
Of course, the generator can be of the type in which the exciter
current is in the stator and still fall within the scope of this
invention.
The alternating current produced in the generator 10 which is
substantially made up of the rotor member 6 and the stator 8 is
rectified by way of a rectifier 12, in accordance with the
structure shown in FIG. 2. The rectified current or rectified
voltage is then converted by means of an inverter 14 into a 3-phase
system at the desired frequency. The three-phase current-voltage
system produced in that way is stepped up in particular in voltage
by means of a transformer 16 to be fed into a connected power
network 18. In some systems, it would be possible to omit the
transformer or to replace it by a choke. Usually however the
voltage requirements in the network 18 are such that it is
necessary to step it up by means of a transformer.
Control is effected by using a main control 20 which can also be
referred to as the main control unit and which forms the
highest-level regulating and control unit of the wind power
installation. The main control 20 acquires its information inter
alia about the network frequency from the subordinated network
measuring unit 22. The main control 20 controls the inverter 14 and
the rectifier 12. It will be appreciated that in principle it would
also be possible to use an uncontrolled rectifier. In addition the
main control 20 controls a direct current setting member 24 for
feeding the exciter current into the rotor member 6 which is part
of the generator 10. The main control 20 modifies inter alia the
power feed into the network or the working point of the generator
when the network frequency falls below a predetermined network
frequency limit value. As the generator is operated in rotary
speed-variable fashion the feed into the network is effected as
described with a full-wave converter formed substantially by the
rectifier 12 and the inverter 14.
In operation the network voltage and the network frequency is
permanently subjected to three-phase measurement by the network
measuring unit 22. A new value for one of the three phase voltages
is afforded from the measurement operation every 3.3 ms--in the
case of a network frequency of 50 Hz. The network frequency is thus
detected each voltage half-wave, filtered and compared to the
preset limit values. For a 60 Hz system, a value for one of the
three phase voltages would be available approximately for every 2.7
ms, more specifically approximately at each zero crossing.
FIG. 3 shows a diagrammatic example of a frequency configuration
and frequency ranges in relation to time, also showing an
associated power configuration.
It will be seen from FIG. 3 that the main control distinguishes in
respect of frequency between three operating ranges, mainly the
deadband range 30, the control band range 32 and the underfrequency
range 34. The deadband range is the frequency range between the
rated frequency f.sub.norm or f.sub.N and the deadband frequency
f.sub.deadband therebeneath. The rated frequency is usually fixedly
predetermined such as for example 50 Hz for the European network
system or 60 Hz in the US area. The deadband frequency
f.sub.deadband can be adjusted whereby the deadband range can at
any event be adjusted in relation to that lower limit. No power
increase is provided in the deadband range.
The control band range 32 extends between the deadband frequency
f.sub.deadband and the subjacent control band frequency
f.sub.controlband. The control band range can be suitably set by
predetermining both the deadband frequency f.sub.deadband and also
the control band frequency f.sub.controlband. In the control band
range, that is to say when the actual frequency assumes values in
the control band range, an increase in the effective power can be
effected in dependence on the frequency deviation, more
specifically in particular the actual frequency from the deadband
frequency, by a power increase P.sub.increase. In that case there
is an effective power increase which is dependent in particular
proportionally on the frequency deviation. Thus the effective power
increase P.sub.increase is also a variable parameter of the control
band range. There can thus be an increase in the effective power in
dependence on the frequency deviation by an additional power
P.sub.increase of 0% to a preset value
P.sub.increase.sub.--.sub.set. The maximum increase in the
effective power can be preset by means of
P.sub.increase.sub.--.sub.set, wherein
P.sub.increase.sub.--.sub.set can be increased from 0% to
P.sub.increase.sub.--.sub.max in 1% steps.
The underfrequency range 34 extends downwardly from the control
band frequency f.sub.controlband. When the actual frequency is
below the control band frequency f.sub.controlband then the maximum
preset power increase is implemented in the underfrequency range.
The power increase P.sub.increase thus assumes the maximum value
which can be for example 10% of the rated power.
FIG. 3 shows in bold the configuration by way of example of the
actual frequency. The configuration of the actual frequency is
identified by reference 36. The frequency initially has the value
of the rated frequency f.sub.norm which it should hold for long
periods of time. If there is a sudden power drain or other problem
in the network, the frequency may drop away at the time t.sub.0. A
configuration by way of example of a power to be set is also
identified by reference 38.
An electric power network, also called the power grid, normally has
a variety of power producing and power control systems in place.
For example, the standard power network includes nuclear power
generators, coal-fired plants, hydro generators, natural gas-fired
plants, and oil-fired plants, as well as wind turbines and other
power generators, all of which place power onto the network.
It is quite important that the network frequencies stay very close
to the target value because all of these power generators are
producing power at the set frequency, such as 50 Hz. If the network
frequency begins to fall slightly, in to the deadband of FIG. 3,
other power generators or systems may take action to correct this
frequency. For example, a nuclear power generator or hydro plant
may increase their power output or take other steps to return the
frequency to exactly 50 Hz. Thus, in many instances, the frequency
will fall into the deadband and then within a short period of time,
less than 1 second, be brought back to the normal frequency where
it will stay for long periods of time. Thus, under most
circumstances, the frequency will not fall below the deadband
because the frequency is kept at or near the normal value by other
power systems coupled to the network.
In the event a major power disruption occurs, the frequency may
fall below the deadband zone established for the wind turbines as
shown in FIG. 3. It is to be expected that if this occurs, other
power generators and controls in the network are making an effort
to return the frequency to f.sub.normal. Once the frequency drops
below f.sub.deadband, wind turbines, according to this invention,
will supply more power in an effort to bring the frequency back up
to a normal value, f.sub.normal. Usually, the frequency 36 will dip
below f.sub.deadband for only a short period of time and due to
increased power provided by the wind turbines, the frequency 36
will return to f.sub.normal and not continue down as shown in FIG.
3. It is, thus, to be understood that the example for the frequency
36 curve in FIG. 3 is to show the range of possible examples that
the frequency 36 may pass through and is not a normal operational
condition.
It is to be noted that the power produced by the wind turbine
should be at least 4% of the rated power for that wind turbine
before the control described herein, by way of example, before it
will carry out the desired power increase described herein.
The actual frequency 36 drops away at the time t.sub.0, but is
firstly in the deadband range 30 so that no power increase takes
place. The actual power being produced which is at least 4% of the
rated power, therefore initially remains constant. At the time
t.sub.1 the actual frequency 36 reaches the deadband frequency
f.sub.deadband and falls below same. In the illustrated example the
power 38 rises linearly with the further drop in the frequency 36.
That is to say the power increase P.sub.increase, namely the
respective increase with respect to the initial value P.sub.A, is
here proportional to the difference between the actual frequency 36
and the deadband frequency f.sub.deadband. The proportionality
factor is so set here that the power increase P.sub.increase
reaches its maximum value of 10% of the rated power P.sub.n when
the frequency reaches the control band frequency f.sub.controlband.
That is the case at the time t.sub.2. The power increase
P.sub.increase can thus be specified in principle for the control
band range with:
P.sub.increase=P.sub.increase.sub.--.sub.set.times.P.sub.N.times.(f.sub.d-
eadband-f)/(f.sub.deadband-f.sub.controlband), insofar as further
boundary conditions like also maximum times are observed for a
power increase.
If the frequency 36 falls further below the control band frequency
f.sub.controlband the power 38 cannot be further increased and thus
from the time t.sub.2 firstly remains at a maximum value, namely
the initial value plus the maximum value of P.sub.increase, namely
+10% of the rated power. If the frequency now rises again and at
time t.sub.3 exceeds the value of the control band frequency
f.sub.controlband, the power increase is thus also reduced again
until the frequency 36 rises at the time t.sub.4 above the deadband
frequency f.sub.deadband. At that time t.sub.4 the power has then
reached the initial value P.sub.A again and does not fall any
further.
It is to be emphasized that FIG. 3 shows an idealized configuration
and any regulating dynamics are initially disregarded. As already
noted, in actual operation, the frequency 36 will often return to
the normal value after a short time has passed. In addition, in the
stated example--contrary to the diagrammatic view--the maximum time
for which the power is increased should not exceed 8 sec. It is
precisely in the case of smaller power increases however that a
prolongation of that time can possibly be considered. It is to be
observed that the linear frequency drop and linear frequency rise
shown in FIG. 3 were selected to illustrate the control diagram and
do not necessarily coincide with a frequency characteristic which
is usually to be expected in actual operation of a power supply
network.
FIG. 3 shows a diagram illustrating the configuration of the
network frequency and as the reaction thereto the variation in the
power feed from a wind power installation.
It is moreover to be seen that, at a given time t.sub.1, the
network frequency dips and more specifically below a given
frequency value below the target frequency of about 50 Hz. If the
frequency falls below a frequency value of for example 0.1% below
the target value (and falls still further) the power of the wind
power installation is increased above its currently prevailing
value, for example by 20% of the currently prevailing power or by
up to 30% above the rated power, practically instantaneously, that
is to say in an extremely short time and for a short period, that
is to say within a few ms, for example 50 to 100 ms or also 500 to
1000 ms, to name a further example. The example in FIG. 3 is based
on an increase by 10% in the rated power. In the extreme case, when
the power is just 4% of the rated power and is increased to 10% of
the rated power, at least theoretically it would be possible to
implement a power increase by 2.5 times the current power. That can
be justified inter alia on the basis that, even with a low power
delivery, a comparatively high rotary speed and thus a
correspondingly large amount of rotational energy is already
stored. Thus for example at 4% rated power it is already possible
to reach a rotary speed of about 50% of the rated speed.
If many wind power installations behave as described hereinbefore
then a large amount of additional power is very quickly made
available, with the consequence that the producer/consumer
imbalance is very quickly compensated, with the further consequence
that the network frequency rises further very quickly and even
quickly exceeds its target value.
In the illustrated embodiment the increased power feed into the
network is effected only for about 2 to 10 sec, preferably only
about up to 3 sec, depending on how the frequency behaves.
If for example the frequency rises very quickly again then the
increased power feed can also be rather reduced again and concluded
while in contrast the increased power feed is effected for longer
if the underfrequency power feed remains for a longer period of
time.
FIG. 4 also shows the increased power feed for the situation in
which the power fluctuates, for example because the wind overall is
fluctuating. In addition FIG. 4 also otherwise concerns a
configuration based on a behavior which is really to be
expected.
The frequency 36 is firstly at the rated frequency, namely 50 Hz.
At a time t.sub.0* the frequency 36 then falls off very quickly and
also quite soon falls below the deadband frequency f.sub.deadband.
FIG. 4 admittedly also involves the situation where the frequency
falls below the deadband frequency, but that is detected only after
the frequency has fallen below the selected deadband frequency
after a detection time .DELTA.t.sub.detect, wherein that detection
time is at a maximum 20 ms. The underfrequency is thus detected at
time t.sub.1* as shown in FIG. 4 and the power 38 is thereupon
increased. An increase time .DELTA.t.sub.increase of .ltoreq.800 ms
elapses up to the maximum power increase of P.sub.increase of 10%
rated power above the power still prevailing at the time t.sub.1*.
When the frequency falls below the selected deadband frequency
f.sub.deadband the main control, by virtue of internal control
functions, provides for a power increase P.sub.increase of a
maximum of 10% of the rated power of the wind power installation
from the generator for a preset time t.sub.max. The recognition
time for the underfrequency is less than 20 ms. The level of the
additional power P.sub.increase is proportionally dependent on the
set maximum permissible power increase and the frequency deviation.
The power is increased with a fixed gradient of about 250
kW/s--insofar it is considered at any event on the basis of the
frequency deviation. In that way, in the case illustrated here, a
power increase to the maximum value of a maximum of 10% of the
rated power of the wind power installation is achieved in
.ltoreq.800 ms. The power increase P.sub.increase is available over
a time of a maximum of 8 sec. After at the latest 8 sec, the
effective power of the wind power installation in the illustrated
example is restored at about 250 kW/s to the normal, in particular
previous working point.
Therefore, viewed from the time t.sub.1*, the maximum power
increase is thus achieved after about 800 ms at the time t.sub.2*.
The maximum increased power which is now set is held until the time
t.sub.3* in order then to gradually fall again until the time
t.sub.4* to approximately the initial value or, in dependence on
wind, to a new value. The time from t.sub.1* to t.sub.4*, which can
also be referred to as tmax.sub.P-increase, is a maximum of 8 sec
for the illustrated example. It is to be noted that FIG. 4 is also
a diagrammatic view and precise values including precise time
values cannot be exactly read off therein.
It is to be observed that the frequency 36 rises again during the
power increase, in particular after the time t.sub.2*, and this can
also be attributed to the power increase, that is to say to the
power which is additionally fed into the network. Nonetheless that
crucially depends on the respective network and the respective wind
power installation, and in particular on whether still further wind
power installations implement such a power feed into the network.
Incidentally in the illustrated example however the frequency does
not rise to the rated frequency again within the power increase
range. Nonetheless, by virtue of the maximum time achieved, the
power increase is reduced and concluded.
For the increased power feed into the network, the wind power
installation according to the invention uses the rotational energy
stored in the rotating system comprising the rotor/generator, by
virtue of the moment of inertia. In other words, due to the
additional amounts of power taken off, above what is actually
predetermined by the power characteristic of the wind power
installation, the overall rotor/generator system admittedly
continues to rotate, but it loses rotational energy and thus, after
the increased power feed into the network, rotates more slowly than
previously because more power was taken from the overall system
than was delivered by the wind.
A brief description of how instantaneous power is added to the
network based on the inertia stored in the rotor assembly will aid
in understanding the operation of the invention. A wind turbine has
the benefit that a rapid increase in the exciter current can
extract some of the rotational inertia from the rotating parts of
the system as will now be explained.
As shown in FIGS. 1 and 2, the rotor blades 4, rotor 2 and rotor
member 6 constitute a large rotating mass, referred to herein as
the rotor assembly. This assembly rotates based on the wind speed,
receiving power from the wind to turn the blades, which causes
rotation of the rotor assembly. As the wind speed increases, more
power is applied to the blades and the rotation speed can increase.
Power is extracted from the rotation by applying the exciter
current from the setting member 24 under control of main control
20. As more exciter current is applied by member 24, more power is
extracted from the rotating blades. Applying more exciter current
to the rotor member 6 to extract more power creates a greater force
to oppose rotation of the rotor and thus requires more force from
the wind to turn the blades. With high wind speeds above a certain
value, the wind turbine generates the maximum designed value of
power for the wind turbine, also called herein the rated power.
During most times of operation, the wind turbine will not be
generating power at the rated power value, but rather will produce
power based on a wind speed less than the highest value. Under
light wind speeds, the wind turbine may generate only 10% of the
rated power, at moderate wind speeds it may generate power at 50%
of the rated power and under high wind conditions, will generate
power at 80% of the rated power. The time periods during which a
wind turbine is operating at rated power will occur only with wind
speeds above a certain value.
For a constant wind speed, the exciter current will normally remain
constant so that the RPM of the wind turbine remains constant. If
the exciter current is rapidly increased, this will extract a large
surge of power from the wind turbine but the power will come from
the inertia of the rotor assembly, namely, from the rotor blades 4,
the rotor 2 and rotor member 6 since the wind speed has not
changed. This will cause the rotor assembly to slow down. If the
exciter current is placed very high and remains there for a long
period of time, all of the inertia of the rotating components,
namely, the rotating blades 4, rotor 2 and rotor member 6 will be
converted to electric power and the blades will stop turning. This
will have the benefit of placing a huge surge of power onto the
network, equal to the total inertia of all the rotating components,
but with the downside that the RPM will go to zero. This is usually
not desired, rather, it is usually preferred to only slow one
particular turbine down by some amount, such as half its current
RPM and if more power is needed then to take some of the needed
power from other wind turbines in the same or other wind parks. The
increased exciter current is therefore only applied for a short
period of time, such as 3 to 6 seconds, to any one wind turbine so
that the RPM does not go to zero, and while it will slow the speed
of that particular turbine, the exciter current is returned to a
lower value so that the RPM can return to its prior value based on
the power from the wind. If more instant power is still needed by
the network, another set of wind turbines in the wind farm can have
some of the inertia in their rotor assemblies converted to electric
power.
The amount of power produced from any rotating wind turbine can be
suddenly increased by a large amount for brief periods of time,
even if the wind speed has not changed. If the wind turbine is
rotating in a light wind and producing power at 10% or 20% of its
rated power, the exciter current can be rapidly increased, causing
the wind turbine to produce between 50% to 150% more power for a
brief period of time. Similarly, if the wind turbine is producing
at its rated power, namely, its maximum designed power output, it
is still possible, for brief periods of time by a rapid increase in
the exciter current, to extract an additional 10% to 30% more power
from the wind turbine by using the inertia of the rotor assembly
for electric power generation.
According to one embodiment, power is extracted from the wind
turbine under control of the operator even though the frequency of
the network has not changed. During certain high power demand
situations, for example in the evening at supper time if many homes
are turning on lights and electric ovens, the wind farm can be
managed to have each wind turbine output a surge of power for about
10 seconds, and then a second wind turbine and then a third, etc.
so that over the period of half and hour or one hour, each wind
turbine in the entire wind farm provides in sequence a 10%-20%
surge of power to boost the overall power output of the entire
windfarm for that one hour higher than would be possible in theory,
based on the wind speed. Then, at the end of this time,
particularly in the evening when less power is consumed by the
homes, the wind turbine blades can regain the energy and return to
full rotational speed with a lower exciter current.
This alternative embodiment is particularly beneficial when high
power use periods are followed by low power consumption. For
example, from 7:00-8:00 p.m. has a relatively high power
consumption, but from midnight to 3:00 am. power consumption is
quite low. Similarly, right at breakfast time as coffee is being
made, lights are first turned on and right at noon in some
communities when everyone go inside for lunch, a brief power surge
of about 30 min is needed, followed by a quiet time in which power
consumption may drop by half. In the past, these variations in
power had to be provided by changes in power output from nuclear
plants, hydro plants, coal fired plants and the like, but with this
invention, the sum the inertia from all wind turbines in a large
wind farm over several hundred wind turbines will exceed the extra
power needed. Therefore, under the control of an operator or
computer control system, the wind farm is managed to transfer the
inertia of the many rotor assemblies of the large group of wind
turbines into electric power and then provide this extra power to
the network at a time of high need, which will then be followed by
a reduced power output while the wind turbines restore their
inertia as they extract power from the wind as it continues to
blow. Thus, while one embodiment is to provide the power surge
based on sensing a frequency drop in the power grid to aid to
restore the system, another embodiment which is quite separate is
to provide the power surge under control of an operator or master
computer system which has the ability to manage power production
from a variety of sources.
The rate and amount of electric power that is extracted from the
inertia of the rotating components can vary based on the rate and
amount of change in exciter current under control of the main
control 20. The tables that follow at the end of the text provide
various examples.
The behavior according to the invention of the wind power
installation however in particular has the result that the critical
under frequency situations are successfully managed or successfully
bridged over by existing wind power installations so that further
network management interventions can be initiated within the
critical period of time of for example 1 to 8 sec, in particular 1
to 3 sec, after the occurrence of the under frequency situation,
and such network management interventions, after the wind power
installation or installations (or entire wind park) has or have fed
its or their additional power into the network, intervene in the
action thereof and successfully support the network. If the under
frequency continues for longer than a preset time, such as 10
seconds and the action of other plants, such as other wind power
installation, hydro plants, nuclear power plants and the like are
not able to bring the frequency back to within the deadband, or if
the frequency drops well below the control band, the wind turbine
will first try to supply power at the current network frequency,
even though it is below the desired value. If the network frequency
continues to drop or stays low for too long, the wind turbine will
separate from the network and stop providing power to the
network.
The technical availability of the power increase P.sub.increase in
the case of a network underfrequency is fundamentally given as from
an instantaneous power P.sub.actual of 4% of the rated power. A
power increase P.sub.increase by 10% with respect to the rated
power is then possible. A power increase of 200 kW for a wind power
installation by way of example is illustrated in principle
hereinafter in FIGS. 5 to 8. In this case 200 kW constitute 10% of
the rated power. In principle, it is possible to select between two
options for the behavior in respect of the power increase during
frequency support, namely between a frequency-dependent power
increase as shown in FIG. 5 and a frequency-dependent and rotary
speed-dependent power increase as shown in FIG. 6.
An embodiment which can also be described by reference to FIG. 4
and the values of which are specified in FIG. 4 can be described as
follows.
In the case of frequency changes to below the deadband the required
power increase occurs with a fixed gradient of about 250 kW/s. A
power increase P.sub.increase of up to 10% of the rated power of
the wind power installation (WPI) is achieved after about 80 ms. In
the case of small frequency changes within the control band and in
the power range below 500 kW the power gradient is slightly reduced
by the generator-induced behavior upon power changes. The power
increase P.sub.increase is available over a time of a maximum of
6.4 s. After at the latest 7 s the effective power of the WPI is
set to the normal working point again at 250 kW/s. The control
stabilization time is dependent on the wind conditions and the
installation rotary speed which is set during the implementation
time. The transition to the feed of power into the network in
normal operation is concluded in about 1 s.
FIG. 5 shows a target power P.sub.order in relation to time for the
situation where no power increase would be implemented. That curve
is also included for the purposes of comparison. An underfrequency
is detected at the time t.sub.8 in FIG. 5 and a power increase of
200 kW is predetermined. That power curve which is basically
represented in an angular configuration is identified by
P.sub.increase. That power P.sub.increase rises at the time t.sub.B
to that value increased by 200 kW and keeps that value constant
until the end time t.sub.E and then falls to the value of the
normal power target curve P.sub.order. The normal power curve
P.sub.order has in the meantime fallen away without that having an
influence on the curve P.sub.increase. The time between the initial
time t.sub.B and the end time t.sub.E is about 8 sec. In addition,
a power curve P.sub.actual is also shown, corresponding to the
actually achieved value of the power fed into the network. As shown
in FIG. 5 therefore the power increase P.sub.increase over the
preset implementation time t.sub.max is proportional to the network
frequency. That corresponds to a power delivery independently of
the rotary speed of the rotor of the wind power installation, that
occurs.
The following should also be additionally explained in relation to
FIG. 5: the power of the wind power installation only depends on
the network frequency during frequency support. In addition, the
power increase P.sub.increase which is required proportionally to
the frequency deviation occurs over the preset implementation time
t.sub.max. The total effective power delivery P.sub.actual is thus
the total of the power in accordance with the rotary speed-power
characteristic at the moment in time of activation of inertia
emulation and required power increase P.sub.increase. The overall
effective power delivery is delimited by the maximum apparent power
of the wind power installation. Those limits of the wind power
installation configurations are shown in the power diagrams in
illustrations 7 to 10.
In regard to the frequency-dependent and rotary speed-dependent
power increase as shown in FIG. 6 the power increase achieved, in
relation to the preset implementation time, is proportional to the
network frequency and also varies in dependence on the rotary speed
that is set in respect of the rotor. In dependence on the wind
speed and the rotor rotary speed, the power increase is provided
adapted to the rotary speed. The nomenclature used in FIG. 6
corresponds to that in FIG. 5 and an underfrequency is detected at
the time t.sub.B and the power increase by about 200 kW is
effected. In the further variation up to the end time t.sub.E the
rotary speed decreases and therewith also the target power, without
having regard to a power increase, namely P.sub.order. The power
increase P.sub.increase maintains approximately a value of 200 kW
above the respective current target power P.sub.order. At the time
t.sub.E the power increase is then ended and the power P.sub.actual
falls to the value of the target power P.sub.order.
In addition as an explanation relating to FIG. 6 attention is
directed to the following: the power of the wind power installation
remains controlled during frequency support with the predetermined
rotary speed-power characteristic in dependence on the wind speed.
The overall effective power delivery P.sub.actual over the preset
implementation time t.sub.max is thus the sum of the currently
prevailing rotary speed-dependent power P and the power increase
P.sub.increase required proportionally to the frequency
deviation.
FIGS. 7 and 8 show measurements or recordings, corresponding to
FIGS. 6 and 5, of the power target value P.sub.ref and the actually
set power value P.sub.actual. In that respect the power target
value P.sub.ref concerns the target power, having regard to the
power increase. The power configurations shown in FIG. 7 correspond
in that respect to a frequency-dependent and rotary speed-dependent
power increase, similarly to that shown in FIG. 6. The power
configurations shown in FIG. 8 correspond to an only
frequency-dependent power increase, similarly to that shown in FIG.
5. It is to be observed that FIGS. 5 to 8 however each represent
their own specific configurations.
FIG. 9 in relation to an embodiment shows various possible
frequency-dependent increases of P.sub.increase in dependence on
the selected value of P.sub.increase.sub.--.sub.set. The three
curves by way of example are identified by P.sub.increase',
P.sub.increase'' and P.sub.increase'''.
The additional power P.sub.increase is proportionally dependent on
the measured frequency deviation below the deadband frequency. The
power increase is increased linearly as from the deadband frequency
f.sub.deadband of 0% to the preset power increase
P.sub.increase.sub.--.sub.set upon reaching the control band
frequency f.sub.deadband. In addition, when required by the network
provider, the preset power increase P.sub.increase.sub.--.sub.set
can be predetermined in 1% steps of the rated power to the maximum
permissible power increase P.sub.increase max, from the rated
power. P.sub.increase.sub.--.sub.set is also not exceeded in the
event of a major frequency deviation. Frequency changes occurring
during the implementation time cause direct adaptations in respect
of the power increase.
The rapid increase in power output can be triggered based on the
frequency of the electrical network dropping by a threshold amount.
This threshold amount can be measured by a number of different
techniques within the scope of this invention. One technique is a
percentage drop from the target value, such as 0.1%, 0.2%, 0.3%,
etc., as stated elsewhere herein. Another technique is an absolute
value drop in frequency, such as a drop of 0.5 Hz, 1.0 Hz, 1.5 Hz,
etc., as stated elsewhere herein. Yet a third technique is a rate
of drop over time, for example, a drop of greater than 0.3 Hz over
less than 0.02 seconds. Namely, the system may be set to trigger on
an absolute value drop of 1.0 Hz, and also may trigger on a drop of
less, such as 0.1 Hz or 0.3 Hz if it occurs rapidly, such as over
0.02 seconds or 0.04 seconds.
The ratio P.sub.increase/P.sub.rated in % can be illustrated, in
dependence on the actual frequency or measured frequency f.sub.meas
and in dependence on the value P.sub.increase.sub.--.sub.set which
is specified in %, with the following formula:
(P.sub.increase/P.sub.rated)[%]=((f.sub.deadband-f.sub.meas)/(f.sub.deadb-
and-f.sub.controlband)).times.P.sub.increase.sub.--.sub.set[%]
Table 1 specifies characteristic values or setting ranges for an
installation by way of example. In principle the deadband frequency
can be identified as f.sub.deadband and the control band frequency
as f.sub.controlband. The power increase can be identified as
P.sub.increase or P.sub.extra and the rated power as P.sub.N or
P.sub.rated. In the line `maximum power increase` it is possible to
select between the use P.sub.extra=constant or
P.sub.extra=variable, in dependence on whether a
frequency-dependent power increase or a frequency-dependent and
rotary speed-dependent power increase is to be used.
TABLE-US-00001 TABLE 1 Frequency measurement Frequency resolution
0.01 Hz Frequency accuracy 0.004 Hz Frequency recognition t = 0.02
s Frequency 40-70 Hz measurement range Frequency range 50 Hz
network 60 Hz network Maximum frequency f.sub.max = 57 Hz f.sub.max
= 67 Hz Rated frequency f.sub.rated = 50 Hz f.sub.rated = 60 Hz
Minimum frequency f.sub.min = 43 Hz f.sub.min = 53 Hz Inertia
emulation at under frequency Maximum implementation time of the 8 s
increase Detection time 0.02 s 50 Hz network 60 Hz network Deadband
frequency f.sub.deadband 49-50 Hz 59-60 Hz Control band frequency
f.sub.controlband 47-50 Hz 57-60 Hz Power increase Power 0-10% with
respect to P.sub.rated increase P.sub.increase set Max. power 10%
with respect to P.sub.rated increase P.sub.increase max Setting
option In steps of 1% with respect to P.sub.rated Normal power
Additional power Max. power from 0% to 4% P.sub.rated P.sub.extra
.apprxeq. 0 increase from 4% to 100% P.sub.rated P.sub.extra =
const P.sub.extra .ltoreq. 10% P.sub.rated from 4% to 100%
P.sub.rated P.sub.extra = variable P.sub.extra .ltoreq. 10%
P.sub.rated Gradient of the power .apprxeq.250 kW/s change dP/dt
Recognition time 0.02 s Rise time [for 200 kW] .apprxeq. 0.8 s Fall
time or control .ltoreq.1.0 s stabilization time s. above Waiting
time to next .gtoreq.2 .times. maximum duration of the increase
increase
If the network frequency falls below a set value, for example 1 Hz
or 2 Hz, the main control unit 20 can cause the inverter 14 to
output power onto the network at its then current frequency namely
1 Hz or 2 Hz below normal, until the frequency of the network
returns to the normal value, at which time the main control 20 will
cause the inverter to match the normal frequency as it outputs
power.
The various embodiments described above can be combined to provide
further embodiments. All of the U.S. patents, U.S. patent
application publications, U.S. patent application, foreign patents,
foreign patent application and non-patent publications referred to
in this specification and/or listed in the Application Data Sheet
are incorporated herein by reference, in their entirety. Aspects of
the embodiments can be modified, if necessary to employ concepts of
the various patents, application and publications to provide yet
further embodiments.
These and other changes can be made to the embodiments in light of
the above-detailed description. In general, in the following
claims, the terms used should not be construed to limit the claims
to the specific embodiments disclosed in the specification and the
claims, but should be construed to include all possible embodiments
along with the full scope of equivalents to which such claims are
entitled. Accordingly, the claims are not limited by the
disclosure.
* * * * *
References